Method of developing photographic emulsions



Patented Nov. i3, @45- METHQD F DEVELOPING PHQTOGRAPMC EMULSIONS No Drawing. Application September 2, 1943, Serial No. 500,924

6 (Jlaims.

This invention relates to photography and particularly to a method for developing photographic emulsions.

In the customary manner of developing exposed gelatino-silver halide emulsions, the film plat or paper carrying the emulsion is developed and then must be fixed, washed and dried. These operations consume a considerable amount of time and in many cases cannot be shortened if a thoroughly washed and stable print is to be produced. It is frequently desirable to obtain a photographic print in the minimum of time after exposure and to have a print which possesses the characteristic of the customary silver image.

It is, therefore, an object of our invention to provide a rapid method for developing photographic emulsions. A further object of our invention is to provide a method for developing photographic emulsions without immersing them in water or other liquid. Other objects will appear from the following description of our invention.

These objects are accomplished by incorporating in a silver halide emulsion layer a photographic developing agent with or without 3. Stabilizing agent, and, after exposure, treating the emulsion with moist alkaline vapors for a sumcient length of time to produce a visible image in the layer.

It is known that certain materials, such as those sensitized with diazonium compounds, can be developed by treatment with alkaline vapors but such materials are relatively slow with respect to exposure time and, when finished, do not possess the characteristics of the usual silver print. Diazo prints are of various colors and cannot ordinarily be obtained in black or gray to resemble a silver print.

The sensitiv material employed according to our invention consists of the usual dispersion of silver halide in a suitable water-permeable carrier such as gelatin. The silver halide may be silver bromide, silver chloride or silver bromoiodide. A fine-grain emulsion, such as a modifled Lippmann type emulsion, is preferably used. After dispersion of the silver halide in the gelatin or other carrier, a suitable amount of a photographic developing agent is added to the emulsion. Any of the customary developing agents such as hydroquinone, Elon, Amidol, p-phenyl enediamine, etc., may be used. Stabilizing agents such as sodium sulilte may also be added to the be varied to obtain the desired results.

An emulsion prepared in this way is sufliciently light-sensitive for exposure in a camera and must be handled as in the case of the ordinary photographic film, that is, it must be protected from the action. of light prior to exposure. After exposure of this material, it is treated, according to our invention, with alkaline vapors such as moist ammonia vapors or vapors produced by heating an aqueous solution of a: volatile amine.

The source of alkali may be an aqueous solution of ammonium hydroxide or an aqueous solution of a volatile amine such as methylamine or ethylamine.

' After treatment of the exposed emulsion with the alkaline vapors for a suflicient length of time to produce a visible image in the material, the emulsion is preferably treated with.acid vapors for a short period of time to stop the developing action. No further treatment of the material is required.

The following example illustrates the preparation of an emulsion for use according to our invention:

An emulsion of silver bromoiodide in gelatin solution is prepared in the customary manner. To a four liter volume of this emulsion, consisting of a 4% gelatin-water sol containing 220 grams of silver bromoiodide, there is added 12 grams of hydroquinone and 6 grams of sodium sulfite. This emulsion is coated on a suitable support, such as glass, film or paper, and dried in the customary manner. It is then ready for exposure and development according to our invention.

After exposure of the sensitive material containing the developing agent, it is subjected to the action of alkaline vapors fora sumcient length of time to produce a visible image in the sensitive layer. We prefer to use ammomacal vapors for this purpose, such as the vapors produced by heating a solution of ammonium hydroxide. In using ammonia the exposed layer may be subjected to the action of the vapor of a 10% ammonia solution at 40 C. for approximately one minute. A 33% solution of methylamine or a 25% solution of ethylamine in water may also be employed, these solutions also being heated to about 40 C. and the vapor is allowed to act on the exposed emulsion for about one minute. The strength of the ammonia in the vapors should be such as is obtained by heating 10 cc. of the solutions to the temperatures indicated and confling the vapors to a volume of about 35 cu. inches.

After treatment of the material with the ,1 aline vapors, the excess ammonia solution is removed from the surface of the layer by allowing a stream of compressed air to play on the surface for a few seconds. The emulsion is then subjected to the action of acid vapors, for example, the action of hydrochloric acid vapors arising from a. 37% solution of hydrochloric acid at 20 C. for approximately 30 seconds. The acid vapors prevent further development by the ammonia and ,complete the processing of the exposed material.

We are aware that there have been many proposals, such as that of Eichengrun U. S. Patent 742,405, granted October 27, 1903, for the incorporation of photographic development agents in silver halide emulsions. In all of these, how ever, the emulsion has been immersed in water or other liquid to effect a development of the exposed material. It is this immersion in liquid which our invention is designed to overcome.

We claim:

l. The method of developing an exposed photographic material containing a sensitive silver halide and a photographic silver halide developing agent, which comprises treating said material with moist alkalinevapors for a sumcient length of time to produce a visible image in said material.

2. The method of developing an exposed photographic material containing a sensitive silver halide and a photographic silver halide developing agent, which comprises treating said material with moist ammoniacal vapors for a sufficient length of time to produce a visible image in said material.

3. The method of developing an exposed photographic material containing a sensitive silver halide anda photographic silver halide developing agent, which comprises treating said material with moist ammoniacal vapors for a suilicient length of time to produce a visible image in said material, then treating said material with. acid vapors for a short Period of time.

4. The method of developing an exposed photographic material containing a sensitive silver halide and a photographic silver halide developing agent, which comprises subjecting said exposed material to the action of the vapors from a 10% solution of ammonia at about C. for approximately one minute.

5. The method of developing an exposed gelatino-silver halide emulsion layer containing a photographic silver halide developing agent, which comprises subjecting said exposed layer to the action of the vapors from an ammoniacal solution at about 40 C. for approximately one minute, removing the excess ammonia from the layer and treating the layer with acid vapors 

